Coated particles, methods for their manufacture and for their use as proppants

ABSTRACT

Disclosed are coated particles. The coated particles include substrate particles and a coating disposed over at least a portion of the substrate particles. The coating includes a condensation reaction product of a reaction mixture that includes a liquid isocyanate-functional component and an isocyanate-reactive composition. Also disclosed are methods for making such particles and methods for using such particles as proppants in hydraulic fracturing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of U.S.application Ser. No. 16/459,720 filed Jul. 2, 2019, which is adivisional of and claims the benefit of U.S. application Ser. No.15/682,595 filed Aug. 22, 2017, now U.S. Pat. No. 10,385,261, each ofwhich are incorporated herein by reference in their entirety.

FIELD

The present specification relates to coated particles, methods for theirpreparation and methods of using such particles as proppants inhydraulic fracturing.

BACKGROUND

Hydraulic fracturing is a process in which an underground geologicformation that is disposed adjacent to a bore hole is fractured byinjecting a pressurized material in order to extract a desiredsubstance, such as oil and/or a gas (such as natural gas), from thegeologic formation. The injection of the pressurized material createschannels, i.e., fractures, in the geologic formation through which thedesired substance may flow to the bore hole and be retrieved. In thisprocess, the material injected into the geologic formation is often aliquid carrying solid particles that are often referred to as aproppant. Proppants are often particles, such as sand, that have acoating disposed on the particle. The proppant migrates into thefractures that are formed and holds them open so that the desiredmaterial can flow out of the fracture.

One problem for many existing proppants, particularly those used in lowtemperature (no more than 150° F.) wells, is that of inadequate crushresistance. Crush resistance refers to the ability of a proppant toresist breaking down at high pressure. A proppant with poor crushresistance would fail to effectively prop open fractures in the geologicformation and can contribute to the inclusion of dust particles inextracted fuel substance. Yet another problem, even with proppants thatinitially exhibit good crush resistance, is their inability to maintainsuch good crush resistance over time. In other words, they exhibit poorshelf-life stability.

In addition, materials derived from renewable resources are becomingmore commercially desirable due partly to the increasing cost ofpetroleum-derived feedstocks. The “green” image of renewable-basedproducts has also become a significant factor in the marketing ofvarious products; however, the physical characteristics and propertiesof, for example, any coated proppants produced using such materialsshould not be detrimentally effected as compared to those produced frompetroleum-based materials. In addition, retailers and governmentagencies are pushing for higher renewable resource content in thefinished goods they sell or purchase to take advantage of this “green”image or to reduce the dependence on petroleum-based materials.

As a result, it would be desirable to provide improved coated particlesthat can be used, for example, as a proppant in hydraulic fracturing inwhich the proppant has good crush resistance as measured by unconfinedcompressive strength (“UCS”) and also has the ability to retain its UCSover a significant period of time, i.e., it has extended shelf lifestability. Moreover, it would be further desirable to provide suchparticles in which the coating is derived from a significant amount ofbiobased/renewable material.

The inventions described in this specification were made in view of theforegoing.

SUMMARY OF THE INVENTION

In certain respects, the present specification is directed to coatedparticles comprising: (a) substrate particles having a particle size ofno more than 3 mesh; and (b) a coating disposed over at least a portionof the particles, wherein the coating comprises a condensation reactionproduct of a reaction mixture comprising: (i) a methylene diphenyldiisocyanate mixture comprising at least 10 percent by weight of2,4′-methylene diphenyl diisocyanate and/or 2,2′-methylene diphenyldiisocyanate, based on the total weight of the mixture; and (ii) anisocyanate-reactive composition comprising: (A) a plant oil polyesterpolyol; (B) an aromatic diamine; and (C) a catalyst for the reactionbetween hydroxyl groups and isocyanate groups.

In other respect, the present specification is directed to coatedparticles comprising: (a) substrate particles having a particle size ofno more than 3 mesh; and (b) a coating disposed over at least a portionof the particles, wherein the coating comprises (1) a condensationreaction product of a reaction mixture comprising: (i) a liquidisocyanate-functional component; and (ii) an isocyanate-reactivecomposition comprising: (A) a polyol, such as a plant oil polyesterpolyol, as described above; (B) an aromatic diamine; (C) a catalyst forthe reaction between hydroxyl groups and isocyanate groups; and (2) acrystalline or semicrystalline polyester/polyurethane having adecrystallization temperature of at least 35° C.

The present specification also relates to, for example, methods formaking such coated particles and methods for using such coatedparticles, such as in hydraulic fracturing a geologic formation.

DETAILED DESCRIPTION

Various embodiments are described and illustrated in this specificationto provide an overall understanding of the structure, function,properties, and use of the disclosed inventions. It is understood thatthe various embodiments described and illustrated in this specificationare non-limiting and non-exhaustive. Thus, the invention is not limitedby the description of the various non-limiting and non-exhaustiveembodiments disclosed in this specification. The features andcharacteristics described in connection with various embodiments may becombined with the features and characteristics of other embodiments.Such modifications and variations are intended to be included within thescope of this specification. As such, the claims may be amended torecite any features or characteristics expressly or inherently describedin, or otherwise expressly or inherently supported by, thisspecification. Further, Applicant(s) reserve the right to amend theclaims to affirmatively disclaim features or characteristics that may bepresent in the prior art. Therefore, any such amendments comply with therequirements of 35 U.S.C. § 112 and 35 U.S.C. § 132(a). The variousembodiments disclosed and described in this specification can comprise,consist of, or consist essentially of the features and characteristicsas variously described herein.

Any patent, publication, or other disclosure material identified hereinis incorporated by reference into this specification in its entiretyunless otherwise indicated, but only to the extent that the incorporatedmaterial does not conflict with existing definitions, statements, orother disclosure material expressly set forth in this specification. Assuch, and to the extent necessary, the express disclosure as set forthin this specification supersedes any conflicting material incorporatedby reference herein. Any material, or portion thereof, that is said tobe incorporated by reference into this specification, but whichconflicts with existing definitions, statements, or other disclosurematerial set forth herein, is only incorporated to the extent that noconflict arises between that incorporated material and the existingdisclosure material. Applicant(s) reserves the right to amend thisspecification to expressly recite any subject matter, or portionthereof, incorporated by reference herein.

In this specification, other than where otherwise indicated, allnumerical parameters are to be understood as being prefaced and modifiedin all instances by the term “about”, in which the numerical parameterspossess the inherent variability characteristic of the underlyingmeasurement techniques used to determine the numerical value of theparameter. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter described in the present description should atleast be construed in light of the number of reported significant digitsand by applying ordinary rounding techniques.

Also, any numerical range recited in this specification is intended toinclude all sub-ranges of the same numerical precision subsumed withinthe recited range. For example, a range of “1.0 to 10.0” is intended toinclude all sub-ranges between (and including) the recited minimum valueof 1.0 and the recited maximum value of 10.0, that is, having a minimumvalue equal to or greater than 1.0 and a maximum value equal to or lessthan 10.0, such as, for example, 2.4 to 7.6. Any maximum numericallimitation recited in this specification is intended to include alllower numerical limitations subsumed therein and any minimum numericallimitation recited in this specification is intended to include allhigher numerical limitations subsumed therein. Accordingly, Applicant(s)reserves the right to amend this specification, including the claims, toexpressly recite any sub-range subsumed within the ranges expresslyrecited herein. All such ranges are intended to be inherently describedin this specification such that amending to expressly recite any suchsub-ranges would comply with the requirements of 35 U.S.C. § 112 and 35U.S.C. § 132(a).

The grammatical articles “one”, “a”, “an”, and “the”, as used in thisspecification, are intended to include “at least one” or “one or more”,unless otherwise indicated. Thus, the articles are used in thisspecification to refer to one or more than one (i.e., to “at least one”)of the grammatical objects of the article. By way of example, “acomponent” means one or more components, and thus, possibly, more thanone component is contemplated and may be employed or used in animplementation of the described embodiments. Further, the use of asingular noun includes the plural, and the use of a plural noun includesthe singular, unless the context of the usage requires otherwise.

As indicated, certain embodiments of the present specification aredirected to coated particles. As used herein, the terms “particle” and“particulate” may be used interchangeably and, in each case, refers todiscrete three dimensionally shaped objects. The particles suitable foruse herein can have any of a variety of shapes, including, for example,generally spherical or elongated. In certain embodiments, the particleshave an aspect ratio of from 1:1 (a perfect sphere) up to 1:100, up to1:50, up to 1:20, or, in some cases, up to 1:10 or up to 1:5. As usedherein, the “aspect ratio” of a particle is the ratio of the length ofthe shortest dimension of the particle to the length of the longestdimension of the particle.

The coated particles of the present specification comprise a substrateparticle. The substrate particle can be made of any of a variety ofmaterials including, for example, organic and inorganic materials. Incertain embodiments, the substrate particle comprises a material thatrenders the coated particles suitable for use as a proppant in hydraulicfracturing of a geologic formation. As used herein, the term “proppant”refers to particles that are injected into fractures of an undergroundgeologic formation, such as those that may surround a bore hole, such asa bore hole connected with an oil well, water well, gas well, and thelike, to support the fracture in an open position in order to allow adesired material, such as oil, water, natural gas, or other material, toflow through the fracture to the bore hole for retrieval.

In some embodiments, the substrate particle has a particle size of nomore than 3 mesh (6730 μm), no more than 6 mesh (3360 μm), no more than10 mesh (2000 μm), no more than 20 mesh (841 μm), no more than 40 mesh(400 μm), or, in some cases, no more than 50 mesh (297 μm), no more than60 mesh (250 μm), no more than 70 mesh (210 μm), no more than 80 mesh(177 μm), no more than 100 mesh (149 μm), no more than 200 mesh (74 μm),or, in some cases, no more than 400 mesh (37 μm). In some embodimentswherein the substrate particle comprises sand, for example, the particlesize is no more than 40 mesh (400 μm), or, in some cases, no more than50 mesh (297 μm) or no more than 60 mesh (250 μm). As used herein,“mesh” refers to USA Standard Testing screen numbers. As used herein,“particle size” refers to the largest dimension of a discrete individualparticle (as opposed to an agglomeration of individual particles).

As indicated, the substrate particle may comprise any of a variety ofmaterials, including organic and inorganic materials. In certainembodiments, the substrate particle comprises an inorganic material,such as a clay, graphite, glass, cenosphere, slag, sand, mineral fiber,and/or ceramic. In certain embodiments, the substrate particle comprisesan organic material, such as an organic polymer and/or a naturallyoccurring organic material.

The particles described in this specification may be free-flowingparticles. As used herein, “free-flowing particle” refers to a driedparticle that is not an aggregate of particles stuck or adhered to eachother so as to form clumps. In some embodiments, “free-flowingparticles” of the present specification have an angle of repose that isless than, for example, 60° degrees when the particles are passedthrough a 10 mesh (2000 μm) sieve. Moreover, in some embodiments, thefree-flowing particles of the present specification are such that atleast 85% by weight, such as at least 90% by weight, or, in some cases,at least 95% by weight, of the particles are pourable after 1 week at140° F./95% relative humidity.

Certain embodiments of the present specification are directed to coatedparticles comprising a coating disposed over at least a portion of theparticle. In certain embodiments, the coating is a substantiallycontinuous film that covers all or substantially all the surface of thesubstrate particle. As used herein, “substantially all” means that thecoating covers at least 90 percent of the surface of the substrateparticle. As will be appreciated, the coated particles of the presentspecification are distinct from situations in which particles are simplydispersed in a polymer matrix or binder.

Certain embodiments of the particles of the present specificationcomprise a coating that comprises a condensation reaction product of areaction mixture comprising: (i) a liquid isocyanate-functionalcomponent; and (ii) an isocyanate-reactive composition.

For example, in some embodiments of the particles of the presentspecification, the liquid isocyanate-functional component comprises amethylene diphenyl diisocyanate mixture. As used herein, the term“methylene diphenyl diisocyanate mixture” refers to a mixture of variousisomers of methylene diphenyl diisocyanate monomer (“MDI”), such asmixtures of at least two of 2,2′-MDI, 2,4′-MDI, and 4,4′-MDI, which maybe present in combination with other isocyanate-functional components,such as polymeric methylene diphenyl diisocyanate (“p-MDI”).

More specifically, in certain embodiments of the particles of thepresent specification, the methylene diphenyl diisocyanate mixturecomprises a relatively high amount of 2,2′-MDI and/or 2,4-MDI, in somecases a relatively high amount of 2,4′-MDI. Even more specifically, incertain embodiments, such methylene diphenyl diisocyanate mixturescomprise at least 10 percent by weight, such as at least 15 percent byweight, of 2,4′-MDI and/or 2,2′-MDI, in some cases 2,4′-MDI, based onthe total weight of the mixture. In some embodiments, such methylenediisocyanate mixtures comprise at least 25 percent by weight of 2,4′-MDIand/or 2,2′-MDI, in some cases 2,4′-MDI, based on the total weight ofMDI in the mixture. In fact, it was discovered, unexpectedly, that theuse of such methylene diphenyl diisocyanate mixtures comprising arelatively high amount of 2,2′-MDI and/or 2,4′-MDI, particularly2,4′-MDI, could provide proppant particles of the present specificationthat exhibit very high (more than 75%, in some cases, 90% or more) % UCSretention when measured as described in the Examples.

Such methylene diphenyl diisocyanate mixtures having a relatively highamount of 2,2′-MDI and/or 2,4-MDI are commercially available, andinclude, for example, Mondur® MRS-2, Mondur® MRS-4, Mondur® MRS-5, andMondur® ML, from Covestro LLC.

In some embodiments of the particles of the present specification, theliquid isocyanate-functional component comprises a urethane-modifieddiphenylmethane diisocyanate prepolymer that is prepared by reacting anexcess of a polymethylene poly(phenyl isocyanate) with anisocyanate-reactive component to form the isocyanate-terminatedprepolymer. Suitable isocyanate-reactive components for use in preparingthe liquid urethane-modified diphenylmethane diisocyanate prepolymerinclude polyether polyol and polyester polyols, for example.

In some embodiments, for example, the isocyanate-reactive component usedto produce the liquid urethane-modified isocyanate-terminated prepolymercomprises a polyester polyol. In these embodiments, theisocyanate-terminated prepolymer is produced by reacting a polymericdiphenylmethane diisocyanate having, for example, an isocyanate contentof from 29 to 33.5%, such as 31 to about 32.5% and/or a viscosity at 25°C. of 50 to 1,000 mPa·s, such as 100 to about 350 mPa·s or 150 to 220mPa·s with a polyester polyol or a blend of polyols that comprises apolyester polyol. In some embodiments, the polymeric diphenylmethanediisocyanate employed includes 38 to 50% by weight (based on totalweight of isocyanate) of monomeric diphenylmethane diisocyanate, such as42 to 48% by weight of monomeric diphenylmethane diisocyanate, with theremainder of the polymeric diphenylmethane diisocyanate being made up ofthe higher oligomers of diphenylmethane diisocyanate.

Various commercially available polymeric diphenylmethane diisocyanatesmay be used. Examples of suitable polymeric diphenylmethanediisocyanates which are commercially available include those sold underthe names Mondur® MR and Mondur® MR Light by Covestro LLC.

In these embodiments, the polymeric diphenyl-methane diisocyanate isreacted with a polyol, such as a polyester polyol, or a polyol blendcomprising a polyester polyol having a functionality of from 1.8 to 4,such as 1.8 to 2.4 or 1.9 to 2.2. Such polyols or polyol blends oftenhave a number average molecular weight (as determined by end groupanalysis) of from 400 to 2,000, such as 400 to 800 or 450 to 500.

Suitable polyester polyols for preparing liquid urethane-modifieddiphenylmethane diisocyanate prepolymers suitable for use herein includethe reaction products of polyhydric alcohols (preferably dihydricalcohols to which trihydric alcohols may be added) with polybasic(preferably dibasic) carboxylic acids, the corresponding carboxylic acidanhydrides and polycarboxylic acid esters of lower alcohols or mixturesthereof. The polycarboxylic acids may be aliphatic, cycloaliphatic,aromatic and/or heterocyclic and they may be substituted, e.g., byhalogen atoms, and/or unsaturated.

Examples of suitable polycarboxylic acids include: succinic acid; adipicacid; suberic acid; azelaic acid; sebacic acid; phthalic acid;isophthalic acid; trimellitic acid; phthalic acid anhydride;tetrahydrophthalic acid anhydride; hexahydrophthalic acid anhydride;tetrachlorophthalic acid anhydride; endomethylene tetrahydrophthalicacid an hydride; glutaric acid anhydride; maleic acid; maleic acidanhydride; fumaric acid; dimeric and trimeric fatty acids such as oleicacid, which may be mixed with monomeric fatty acids; dimethylterephthalates and bis-glycol terephthalate.

Suitable polyhydric alcohols include: ethylene glycol; 1,2- and1,3-propylene glycol; 1,3- and 1,4-butylene glycol; 1,6-hexanediol;1,8-octanediol; neopentyl glycol; cyclohexanedimethanol;(1,4-bis-(hydroxy-methyl)cyclohexane); 2-methyl-1,3-propanediol;2,2,4-trimethyl-1,3-pentanediol; triethylene glycol; tetraethyleneglycol; polyethylene glycol; dipropylene glycol; polypropylene glycol;dibutylene glycol and polybutylene glycol, glycerine andtrimethylolpropane.

The polyesters may also contain a portion of carboxyl end groups.Polyesters of lactones, e.g., ε-caprolactone or hydroxyl carboxylicacids such as ω-hydroxycaproic acid, may also be used.

In some embodiments, the polyester polyol is formed from ethylene glycoland/or diethylene glycol and phthalic acid anhydride,dimethylterephthalate or phthalic acid.

Polyester polyols and polyester polyol blends of the type disclosed inU.S. Pat. No. 4,644,027 in which a hydrophobic compound is incorporatedinto the polyester polyol are suitable.

As indicated, the liquid urethane-modified diphenylmethane diisocyanateprepolymers can be made by reacting the polymeric diphenylmethanediisocyanate with the polyester polyol in amounts such that theequivalent ratio of isocyanate groups in the polymeric diphenylmethanediisocyanate to hydroxyl groups in the polyester polyol is from, forexample, 15:1 to 160:1, such as 25:1 to 39:1. This reaction is oftencarried out at temperatures of from about 40 to about 80° C., such as 50to 60° C. for periods of, for example, from 10 to 60 minutes, such as 20to 40 minutes.

In some embodiments, such liquid urethane-modified diphenylmethanediisocyanate prepolymers have an NCO functionality of at least 2.1, suchas at least 2.3 or at least 2.5 and less than or equal to 3.8, such asless than or equal to 3.5 or less than or equal to 3.2. Such liquidurethane-modified diphenylmethane diisocyanate prepolymers may have anNCO functionality ranging between any combination of these upper andlower values, inclusive, e.g. from 2.1 to 3.8, such as from 2.3 to 3.5or from 2.5 to 3.2.

In some embodiments, such liquid urethane-modified diphenylmethanediisocyanate prepolymers have an NCO group content of at least 25% byweight, such as at least 27.5% by weight or at least 29% by weight andan NCO group content of less than or equal to 33% by weight, such asless than or equal to 32% by weight or less than or equal to 31% byweight. Such liquid urethane-modified diphenylmethane diisocyanateprepolymers may have an NCO group content ranging between anycombination of these upper and lower values, inclusive, e.g., from 25%to 33% by weight, from 27.5% to 32% by weight or from 29% to 31% byweight.

In some embodiments, such liquid urethane-modified diphenylmethanediisocyanate prepolymers have an NCO group content of from 27.5% to 32%,such as 29.8 to 31.2%, and a functionality of from 2.3 to 3.5, such as2.8, and a viscosity of 200 to 1000 mPa·s at 25° C., such as 235 to 435mPa·s at 25° C.

In other embodiments, the isocyanate-reactive component used to producethe liquid urethane-modified isocyanate-terminated prepolymer comprisesa branched aliphatic dihydroxy compound. For example, in someembodiments, the liquid urethane-modified isocyanate-terminatedprepolymer comprises the reaction product of 0.1 to 0.3 mols of analiphatic dihydroxy compound having a branched carbon chain with 1 molof 4,4′-diphenylamine diisocyanate and/or the 2,4′-isomer thereof.

Suitable branched aliphatic dihydroxy compounds for preparing suchliquid urethane-modified isocyanate-terminated prepolymers include, forexample, 1,3-propanediols which contain at least two alkyl groups in themolecule, such as 2-ethylhexyldiol-(1,3), 2-methyl pentandiol-(2,4),2,2,4-trimethylpentanediol-(1,3), 3-methyl-5-ethylheptane diol-(2,4),2-methyl-2-propylpropane diol-(1,3), or mixtures of any two or morethereof. In certain embodiments, poly-1,2 propylene ether glycols ofmolecular weight 134 to 700, such as dipropylene glycol, tripropyleneglycol, a polypropylene glycol, or mixtures of any two or more thereof,are used.

Such liquid urethane-modified isocyanate-terminated prepolymers can beprepared by introducing the branched aliphatic glycols into thediisocyanate at a temperature of 40 to 600° C. with stirring, theaddition reaction being completed at temperatures of up to 800° C.

In certain embodiments, the isocyanate content of such liquidurethane-modified isocyanate-terminated prepolymers the products of theprocess amounts to 15% NCO to 25% NCO. The difference between theisocyanate content of the pure crystalline diphenylmethane diisocyanateand that of the products of the process corresponds to the amount ofbranched dihydroxyl compounds employed.

In some embodiments, such liquid urethane-modified diphenylmethanediisocyanate prepolymers have an NCO group content of at least 15% byweight, such as at least 20% by weight or at least 22% by weight and anNCO group content of less than or equal to 25% by weight, such as lessthan or equal to 24% by weight or less than or equal to 23% by weight.Such liquid urethane-modified diphenylmethane diisocyanate prepolymersmay have an NCO group content ranging between any combination of theseupper and lower values, inclusive, e.g., from 15% to 25% by weight, from20% to 24% by weight or from 22% to 24% by weight.

In some embodiments, such liquid urethane-modified diphenylmethanediisocyanate prepolymers have a viscosity of 300 to 1000 mPa·s at 25°C., such as 500 to 1000 mPa·s at 25° C., or 550 to 800 mPa·s at 25° C.at 25° C.

As indicated, certain embodiments of the particles of the presentspecification comprise a coating that comprises a condensation reactionproduct of a reaction mixture comprising an isocyanate-reactivecomposition. As used herein, the term “isocyanate-reactive composition”refers to a composition that includes components with functional groupsreactive towards isocyanate groups (“isocyanate-functionalcomponent(s)”), such as hydroxyl groups, amine groups, and thiol groups.

In certain embodiments, the isocyanate reactive composition comprises aplant oil polyester polyol. As used herein, the term “plant oilpolyester polyol” refers to an ester polyol produced by introducingactive hydrogen groups onto a plant oil. As will be appreciated, plantoils are triglycerides of mixtures of fatty acids, often containing someunsaturated fatty acids.

Plant oil polyester polyols suitable for use herein can be produced byany of a variety of methods. For example, in certain embodiments, atwo-step process is used that begins with the epoxidation of plant oilfollowed by introduction of hydroxyl groups onto the plant oil moleculeby opening the oxirane of epoxidized plant oil. This opening of theoxirane ring can be accomplished in a variety of ways, such as forexample, with ricinoleic acid, as described in U.S. Pat. No. 2,882,249,with acrylic acid, as described in U.S. Pat. No. 4,025,477, withcarboxylic acids, as described in U.S. Pat. Nos. 5,266,714 and5,302,626, with acid leached clay, as described in U.S. Pat. No.6,891,053, with (poly)alcohols, as described in U.S. Pat. Nos.4,508,853, 4,742,087, 6,433,125, 4,551,517 and 4,886,893, or with amixture of water, alcohol and fluoroboric acid, as described in U.S.Pat. Nos. 6,107,433, 6,433,121, 6,573,354 and 6,686,435.

In another technique, as described in U.S. Patent ApplicationPublication No. 2009/0292099 A1 at [0015]-[0028], the cited portion ofwhich being incorporated herein by reference, the unsaturated sites in aplant oil are directly functionalized to yield a plant oil polyesterpolyol in a one-step process by reacting a reactant with at least onenucleophilic functional group (such as amines, thiols and phosphines)and at least one active hydrogen group with a plant oil having at onecarbon-carbon double bond.

Suitable plant oils for use in preparing such plant oil polyesterpolyols include, for example, corn oil, soybean oil, rapeseed oil,sunflower oil, sesame seed oil, peanut oil, safflower oil, olive oil,cotton seed oil, linseed oil, walnut oil and tung oil and mixturesthereof. As will be appreciated, soybean oil, for example, containsabout 54 wt. % linoleic acid, 23 wt. % oleic acid, 10 wt. % palmiticacid, 8 wt. % linolenic acid and 5 wt. % stearic acid. On average,soybean oil contains 4.65 sites of unsaturation (olefin groups,carbon-carbon double bonds) per molecule.

In certain embodiments, the plant oil polyester polyol has a viscosityat 25° C. of less than 1000 mPa·s, such as 100 to 1000 mPa·s cps or 200to 500 mPa·s, an OH number of 175 to 550, such as 175 to 340, or 200 to260, and/or a functionality of from 2 to 5, such as 2 to 4,2 to 3, or 2.

In certain embodiments, the plant oil polyester polyol, as describedabove, is present in an amount of at least 50% by weight, such as atleast 60% by weight, such as 50% to 90% by weight, or 60% to 80% byweight, based on the total weight of isocyanate-reactive componentspresent in the isocyanate-reactive composition.

As previously indicated, in certain embodiments, the isocyanate-reactivecomposition also comprises an aromatic diamine, such as those whichcontain at least one alkyl substituent in the ortho-position to a firstamino group and two alkyl substituents in the ortho-position to a secondamino group or mixtures thereof. In some embodiments, at least two ofsaid alkyl substituents contain at least two carbon atoms. In certainembodiments, the reactivity of said diamine towards isocyanates has notbeen reduced by electron attracting substituents, such as halogen,ester, ether or disulphide groups, as is the case, for example, withmethylene-bis-chloroaniline (MOCA). In certain embodiments, suchdiamines do not contain other functional groups reactive withisocyanates. In certain embodiments, the foregoing mentioned alkylsubstituent can have as many as twenty carbon atoms and can be straightor branched long chains.

In certain embodiments, the aromatic diamine contains at least one alkylsubstituent in the ortho-position to a first amino group and two alkylsubstituents having from 1 to 3 carbon atoms in the ortho-position to asecond amino group, provided that two of these alkyl substituentscontain two or three carbon atoms. Examples of such aromatic diaminesinclude: 1-methyl-3,5-diethyl-2,4-diaminobenzene,1-methyl-3,5-diethyl-2,6-diaminobenzene,1,3,5-triethyl-2,6-diaminobenzene, and3,5,3′,5′-tetraethyl-4,4′-diaminodiphenylmethane.

The above-mentioned aromatic amines may, of course, be used as mixtureswith each other or in combination with other active aromatic amines.

In certain embodiments, aromatic diamines which have a linear alkylsubstituent having from 1 to 3 carbon atoms in both ortho-positions toeach amino group, provided that two of the alkyl substituents containtwo or three carbon atoms, are used. In some embodiments, the diamine isliquid at room temperature and miscible with polyols, particularly withpolyether polyols. An example of such a compound is1-methyl-3,5-diethyl-2,4-diaminobenzene or a mixture of this compoundwith 1-methyl-3,5-diethyl-2,6-diaminobenzene.

In certain embodiments, the aromatic amine is present in an amount of 5to 50% by weight, such as 10 to 40% by weight, or, in some cases, 25 to35% by weight, based on the total weight of the total weight ofisocyanate-reactive components present in the isocyanate-reactivecomposition.

As indicated, the isocyanate-reactive composition may comprise acatalyst for the reaction between hydroxyl groups and isocyanate groups.Suitable catalysts include, for example, organic tin compounds such astin (II) salts of carboxylic acids (such as tin (II) acetate, tin (II)octoate, tin (II) ethyl hexoate or tin (II) laurate), and the dialkyltin salts of carboxylic acids (such as dibutyl tin diacetate, dibutyltin dilaurate, dibutyl tin maleate or dioctyl tin diacetate) eitheralone or as a complex with amidines, such as2,3-dimethyl-3,4,5,6-tetrahydropyrimidine or2-methyl-3-cyclohexyl-3,4,5,6-tetrahydropyrimidine, aminopyridines,aminopyrimidines, hydrazino pyridines or hydrazino pyrimidines.

Other catalysts which may be used include tertiary amines, such astriethylamine, tributylamine, N-methylmorpholine, N-ethylmorpholine,N-cocomorpholine, N,N,N′,N′-tetramethyl-ethylenediamine,1,4-diaza-bicyclo-(2,2,2)-octane,N-methyl-N′-dimethylaminoethyl-piperazine, N,N-dimethylbenzylamine,bis-(N,N-diethylamino-ethyl)-adipate, N,N-diethylbenzylamine,pentamethyl-diethylenetriamine, N,N-dimethylcyclohexylamine,N,N,N′,N′-tetramethyl-1,3-butanediamine,N,N-dimethyl-β-phenylethylamine, 1,2-dimethylimidazole and2-methylimidazole.

Tertiary amines having isocyanate-reactive hydrogen atoms include, forexample, triethanolamine, triisopropanolamine, N-methyl-diethanolamine,N-ethyl-diethanolamine, and N,N-dimethyl-ethanolamine may also be used.Reaction products of these compounds with alkylene oxides, such aspropylene oxide and/or ethylene oxide are also suitable.

Silaamines having carbon-silicon bonds as described, e.g. in German Pat.No. 1,229,290 may also be used as catalysts. Examples include2,2,4-trimethyl-2-silamorpholine or1,3-diethylaminomethyl-tetramethyl-disiloxane.

Basic nitrogen compounds, such as tetraalkylammonium hydroxides, alkalimetal hydroxides such as sodium hydroxide, alkali metal phenolates, suchas sodium phenolate, and alkali metal alcoholates, such as sodiummethylate, may also be used as catalysts. Hexahydrotriazines are alsosuitable catalysts.

In certain embodiments, the catalyst comprises (i) an organic tincompound, such as a dialkyl tin salt of carboxylic acid, such as dibutyltin dilaurate, and (ii) a tertiary amine, such as1,4-diaza-bicyclo-(2,2,2)-octane. In certain embodiments, the relativeweight ratio of (i) to (ii) is 20:80 to 80:20, such as 40:60 to 60:40.

In certain embodiments, the catalyst is present in an amount of from0.01 to 10% by weight, such as 0.05 to 1% by weight, based on the totalweight of isocyanate-reactive components in the isocyanate-reactivecomposition.

The catalysts to be used should accelerate the polyaddition reaction tosuch an extent that once the starting components have been mixed thereaction mixture has a flow time (e.g., the capability to flow and hencethe time during which the mixture may still be delivered) of less than15, 10, or 5 seconds.

In certain embodiments, the liquid isocyanate-functional component andthe isocyanate-reactive composition are each used in amounts such thatthe reaction mixture has an NCO Index (i.e., the ratio of the totalnumber of reactive isocyanate groups present to the total number ofisocyanate-reactive groups that can react with the isocyanate multipliedby 100) of at least 120, such at least 140, or at least 180 and no morethan 500, such as no more than 400 or, in some cases, no more than 300or no more than 250. The NCO Index can range between any combination ofthese upper and lower values, inclusive, e.g., from 120 to 500, 140 to500, 180 to 400, 180 to 300, or 180 to 250, for example.

Other ingredients may be used to form the coated particles of thisspecification. For example, in certain embodiments, use is made of anaminosilane coupling agent having the formula:

in which: (A) each X, which may be the same or different, is an organicgroup that is inert to isocyanate groups below 100° C., provided that atleast one of these groups are alkoxy or acyloxy groups, such as whereeach X is an alkyl or alkoxy group having 1 to 4 carbon atoms, such aswhere each X is an alkoxy group having 2 carbon atoms; (B) Y is a linearor branched alkylene group containing 1 to 8 carbon atoms, such as alinear group containing 2 to 4 carbon atoms or a branched groupcontaining 5 to 6 carbon atoms, such as a linear group containing 3carbon atoms; and (C) R¹ is hydrogen or an organic group which is inertto isocyanate groups at a temperature of 100° C. or less, such as analkyl, cycloalkyl, or aromatic group having 1 to 12 carbon atoms, or R¹represents a group corresponding to the formula:—Y—Si—(X)₃in which X and Y have the same meanings described above.

In certain embodiments, each X represents a methoxy, ethoxy, or propoxygroup, and Y is a linear alkylene group containing 3 carbon atoms (i.e.,a propylene group) and R¹ is hydrogen.

In certain embodiments, the aminosilane is used in an amount of 0.1 to10% by weight, such as 1 to 5% by weight, or, in some cases, 2 to 4% byweight, based on the total weight of the isocyanate-reactivecomposition.

Surface-active additives may also be used. Examples include the sodiumsalts of ricinoleic sulphonates or of fatty acids, or salts of fattyacids with amines, such as oleic acid diethylamine or stearic aciddiethanolamine, alkali metal or ammonium salts of sulphonic acids, suchas dodecylbenzene sulphonic acid or dinaphthylmethane disulphonic acid,or of fatty acids, such as ricinoleic acid, or of polymeric fatty acids,and water-soluble polyether siloxanes that have a polydimethylsiloxanegroup attached to a copolymer of ethylene oxide and propylene oxide.

Pigments, dyes, flame retarding agents, stabilizers against ageing andweathering, plasticizers, fungistatic and bacteriostatic substances andfillers may also be used.

In certain embodiments, the coated particles of the presentspecification comprise a coating that comprises a crystalline orsemicrystalline polyester/polyurethane having a decrystallizationtemperature of at least 35° C.

In fact, it was surprisingly discovered that the % UCS retention(measured as described in the Examples) of coated particle proppants ofthe present specification could be dramatically improved by inclusion ofjust a small amount (as described below) of such crystalline orsemicrystalline polyester/polyurethane in the coating. As a result, someembodiments of the coated particles of the present specificationcomprise: (a) a substrate particle having a particle size of no morethan 3 mesh; and (b) a coating disposed over at least a portion of theparticle, wherein the coating comprises (1) a condensation reactionproduct of a reaction mixture comprising: (i) a liquidisocyanate-functional component, such as any of those described above;and (ii) an isocyanate-reactive composition comprising: (A) a polyol,such as polyether polyols and/or polyester polyols, such as the plantoil polyester polyol described above; (B) an aromatic diamine; (C) acatalyst for the reaction between hydroxyl groups and isocyanate groups;and (2) a crystalline or semicrystalline polyester/polyurethane having adecrystallization temperature of at least 35° C.

As used herein, the term “crystalline or semicrystalline” means that apolyester/polyurethane has a degree of crystallization of 5 to 100%,such as 20 to 100%. As used herein, “crystalline” means that, in the DSCof a polymer, with rising temperature, a maximum is passed through,which is caused by the melting of regular substructures in the polymer.The temperature at which this maximum occurs is referred to herein asthe “decrystallization temperature”. In the case of passage through amelting-crystallization cycle, the melting enthalpy can be determinedfrom the area of the melting of crystallization peak. In certainembodiments, the polyester/polyurethanes used herein have a meltingenthalpy of at least 5 J/g, such as at least 20 J/g, or, in some cases,at least 40 J/g.

As used herein, the term “polyester/polyurethane” refers to polymersthat contain a plurality of ester linkages and a plurality of urethanegroups in the polymer backbone. As used herein, “polyurethane” alsoencompasses polyurethane ureas that, in addition to urethane groups,also contain urea groups.

In certain embodiments, the crystalline or semicrystallinepolyester/polyurethane has a decrystallization temperature of at least35° C., such as at least 40° C., at least 42° C., or, in some cases, atleast 45° C. and/or no more than 100° C., no more than 60° C., or, insome cases, no more than 52° C.

In certain embodiments, the crystalline or semicrystallinepolyester/polyurethane has a glass transition temperature of at least−100° C., such as at least −60° C. and/or no more than −10° C., such asno more than −40° C., when measured by DSC in accordance with DIN 65467with a heating up rate of 10 K/min.

In certain embodiments, the crystalline or semicrystallinepolyester/polyurethane has a weight-average molecular weight (Mw) of atleast 20,000 g/mole, such as at least 30,000 g/mole or, in some cases,at least 50,000 g/mole and/or no more than 250,000 g/mole, such as nomore than 220,000 g/mole, or, in some cases, no more than 200,000g/mole. As used herein, the molecular weight of a polymer is determinedby means of gel permeation chromatography (GPC/SEC) withdimethylacetamide as the mobile phase.

In certain embodiments, the crystalline or semicrystallinepolyester/polyurethane comprises a reaction product of a reactionmixture comprising: (a) a di- or poly-functional polymeric polyol with anumber average molecular weight of from 400 to 5,000 g/mole andcomprising a polyester polyol; and (b) a di- or poly-functionalisocyanate component. Furthermore, the polyester/polyurethane may, insome embodiments, be present, i.e., solubilized or dispersed, in anorganic solvent-based composition or an aqueous composition whendeposited onto the substrate particle. As used herein, the term “aqueouscomposition” refers to a composition in which the carrier fluid for thepolyester/polyurethane comprises predominantly water, although thepresence of some volatile organic compounds is not excluded. In certainembodiments of the aqueous composition, water is present in an amount ofat least 80% by weight, such as at least 90% by weight, at least 95% byweight, or, in some cases, at least 98% by weight or at least 99% byweight, based on the total weight of the carrier fluid. As used herein,the term “organic solvent-based composition” refers to a composition inwhich the carrier fluid for the polyester/polyurethane comprisespredominantly a volatile organic compound, although the presence of somewater is not excluded. In certain embodiments of the organicsolvent-based composition, volatile organic compound is present in anamount of at least 80% by weight, such as at least 90% by weight, atleast 95% by weight, or, in some cases, at least 98% by weight or atleast 99% by weight, based on the total weight of the carrier fluid.

In certain embodiments, the proportions of the individual components areselected so that the composition comprising the crystalline orsemicrystalline polyester/polyurethane that is deposited onto thesubstrate particle has a polymer content of 30 to 60 percent by weight,based on the total weight of the composition. In some of theseembodiments, the composition that is deposited onto the substrateparticle also has a viscosity at 25° C. of 20 to 2,000 cps, such as 40to 1,000 cps, or, in some cases, 50 to 600 cps.

As indicated, the crystalline or semicrystalline polyester/polyurethaneof certain embodiments comprises a reaction product of reactantscomprising (a) a di- or poly-functional polymeric polyol with a numberaverage molecular weight of from 400 to 6,000 g/mole, such as 400 to5,000 g/mole, 800 to 3,000 g/mole, or, in some cases, 800 to 2,500g/mole or 1,500 to 2,500 g/mole and comprising a polyester polyol. Asused herein, “poly-functional” means a component that includes three ormore of the functional groups being discussed per molecule, such as, inthe case of a polyol, a component comprising at least three hydroxylgroups in the molecule, such as three or four hydroxyl groups in themolecule and, in the case of an isocyanate, a component comprising atleast three isocyanate groups in the molecule, such as three or fourisocyanate groups in the molecule. In some cases, the di- orpoly-functional polymeric polyol with a number average molecular weightof from 400 to 6,000 g/mole has a hydroxyl equivalent weight of 200 to3,000 g/mole, such as 400 to 1,500 g/mole, or, in some cases, 400 to1,250 g/mole or 750 to 1,250 g/mole.

Polyester polyols suitable for use in such component (a) include, forexample, linear polyester diols and branched polyester polyols. Suitablepolyester diols and polyols include those that can be prepared fromaliphatic, cycloaliphatic and/or aromatic di- or polycarboxylic acids,such as succinic acid, methylsuccinic acid, glutaric acid, adipic acid,pimelic acid, suberic acid, azelaic acid, sebacic acid,nonanedicarboxylic acid, decanedicarboxylic acid, terephthalic acid,isophthalic acid, o-phthalic acid, tetrahydrophthalic acid,hexahydrophthalic acid, cyclohexanedicarboxylic acid, maleic acid,fumaric acid, malonic acid, and/or trimellitic acid, and acidanhydrides, such as o-phthalic anhydride, trimellitic anhydride, and/orsuccinic anhydride, with polyhydric alcohols, such as ethanediol, di-,tri-, or tetra-ethylene glycol, 1,2-propanediol, di-, tri-, ortetra-propylene glycol, 1,3-propanediol, butanediol-1,4, butanediol-1,3,butanediol-2,3, pentanediol-1,5, hexanediol-1,6,2,2-dimethyl-1,3-propanediol (neopentyl glycol),1,4-dihydroxycyclohexane, 1,4-dimethylolcyclohexane, octanediol-1,8,decanediol-1,10, and/or dodecanediol-1,12, optionally with additionaluse of higher-functionality polyols, such as trimethylolpropane,glycerol and/or pentaerythritol. Useful polyhydric alcohols forpreparing the polyester diols and polyols also include cycloaliphaticand/or aromatic di- and polyhydroxyl compounds.

Suitable polyester polyols may also be homo- or copolymers of lactones,which are obtained, for example, by addition of lactones or lactonemixtures, such as butyrolactone, ε-caprolactone, and/ormethyl-ε-caprolactone, onto the suitable difunctional and/orhigher-functionality starter molecules, for example the low molecularweight polyhydric alcohols mentioned above.

In certain embodiments, the di- or poly-functional polyester-polyolcomprises a reaction product of reactants comprising adipic acid and oneor more of butanediol-1,4, hexanediol-1,6, and neopentyl glycol.

In certain embodiments, the di- or poly-functional polyester polyolcomprises a reaction product of reactants comprising a dicarboxylic acidcomprising succinic acid, adipic acid, dodecandoic acid, derivativesthereof, and/or mixtures thereof, employed in an amount of at least 80mole %, at least 85 mole %, or, in some cases, at least 90 mole %, basedon the total amount of all carboxylic acids used to make the polyesterpolyol. In certain embodiments, the di- or poly-functional polyesterpolyol comprises a reaction product of reactants comprising adicarboxylic acid comprising glutaric acid, azelaic acid, 1,4-, 1,3-and/or 1,2-cyclohexanedicarboxylic acid, terephthalic acid, isophthalicacid, derivatives thereof, and/or mixtures thereof, employed in anamount of up to 20 mole %, such as up to 15 mole %, or, in some cases,up to 10 mole %, based on the total amount of all the carboxylic acidsused to make the polyester polyol. In certain embodiments, the di- orpoly-functional polyester polyol comprises a reaction product ofreactants comprising a polyol comprising monoethylene glycol,1,3-propanediol, butanediol-1,4, pentanediol-1,5, hexanediol-1,6,neopentyl glycol and/or a mixture thereof, employed in an amount of atleast 80 mole %, at least 85 mole %, or, in some cases, at least 90 mole%, based on the total amount of all polyols used to make the polyesterpolyol. In certain embodiments, the di- or poly-functional polyesterpolyol comprises a reaction product of reactants comprising a polyolcomprising diethylene glycol, hydroxypivalic acid neopentyl glycol,cyclohexanedimethanol, pentane-1,2-diol, nonane-1,9-diol,trimethylolpropane, glycerol, pentaerythritol, and/or a mixture thereof,employed in an amount of up to 20 mole %, such as up to 10 mole %, basedon the total amount of all the polyols used to make the polyesterpolyol.

In certain embodiments, the di- or poly-functional polyester polyolcomprises: (i) at least 50 percent by weight, such as 60 to 100 percentby weight, 70 to 100 percent by weight, 80 to 100 percent by weight, or,in some cases, 90 to 99 percent by weight, based on the total weight ofthe di- or poly-functional polyester polyol present in the composition,of a polyester polyol comprising a reaction product of reactantscomprising (a) adipic acid (employed in an amount of at least 80 mole %,at least 85 mole %, or, in some cases, at least 90 mole %, based on thetotal amount of all carboxylic acids used to make the polyester polyol);and (b) butanediol-1,4 (employed in an amount of at least 80 mole %, atleast 85 mole %, or, in some cases, at least 90 mole %, based on thetotal amount of all polyols used to make the polyester polyol); and (ii)up to 50 percent by weight, such as up to 40 percent by weight, up to 30percent by weight, up to 20 percent by weight, or 1 to 10 percent byweight, based on the total weight of the di- or poly-functionalpolyester polyol present in the composition, of a polyester polyolcomprising a reaction product of reactants comprising: (a) adipic acid(employed in an amount of at least 80 mole %, at least 85 mole %, or, insome cases, at least 90 mole %, based on the total amount of allcarboxylic acids used to make the polyester polyol); (b) hexanediol-1,6,(employed in an amount of at least 40 mole %, such as 40 to 80 mole %,or, in some cases, 50 to 70 mole %, based on the total amount of allpolyols used to make the polyester polyol) and; (c) neopentyl glycol(employed in an amount of up to 60 mole %, such as 20 to 60 mole %, or,in some cases, 30 to 50 mole %, based on the total amount of all polyolsused to make the polyester polyol).

In some embodiments, in addition to the polyester polyol, such component(a) may include up to 50% by weight, such as up 40%, or, in some cases,up to 30% by weight, based on the total weight of component (a), of adi- or poly-functional polymeric polyol that is different from thepolyester polyol, such as, for example, a polyether polyol and/or apolycarbonate polyol. In some embodiments, however, thepolyester/polyurethane is substantially free, or in some casescompletely free, of polyether units.

As indicated, the crystalline or semicrystalline polyester/polyurethanecomprises a reaction product of reactants that comprises (b) a di- orpoly-functional isocyanate component. Any desired organic compoundswhich have at least two free isocyanate groups per molecule can be usedincluding, for example, diisocyanates according to the structure Y(NCO)₂where Y is a divalent aliphatic hydrocarbon radical having 4 to 12carbon atoms, a divalent cycloaliphatic hydrocarbon radical having 6 to15 carbon atoms, a divalent aromatic hydrocarbon radical having 6 to 15carbon atoms or a divalent araliphatic hydrocarbon radical having 7 to15 carbon atoms. Specific, but non-limiting, examples of suchdiisocyanates are tetramethylene diisocyanate, methylpentamethylenediisocyanate, hexamethylene diisocyanate (“HDI”), dodecamethylenediisocyanate, 1,4-diisocyanatocyclohexane,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (“IPDI”),4,4′-diisocyanatodicyclohexylmethane,4,4′-diisocyanatodicyclohexylpropane-(2,2), 1,4-diisocyanatobenzene,2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene,4,4′-diisocyanatodiphenylmethane, 2,2′- and2,4′-diisocyanatodiphenylmethane, tetramethylxylylene diisocyanate,p-xylylene diisocyanate, p-isopropylidene diisocyanate, and mixtures oftwo or more of these compounds.

Also suitable are higher-functionality polyisocyanates, or modifiedpolyisocyanates, having, for example, carbodiimide groups, allophanategroups, uretdione groups, isocyanurate groups, urethane groups and/orbiuret groups.

In some embodiments, the diisocyanate comprises an aliphatic and/oraraliphatic diisocyanate such as HDI, 1,4-diisocyanatocyclohexane,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane,4,4′-diisocyanatodicyclohexylmethane and/or4,4′-diisocyanatodicyclohexylpropane-(2,2).

In certain embodiments, the crystalline or semicrystallinepolyester/polyurethane comprises a silane-containingpolyester/polyurethane. Thus, in some embodiments, the crystalline orsemicrystalline polyester/polyurethane is a reaction product ofreactants further comprising (c) an alkoxysilane that, depending on theprocess used to make the polyester/polyurethane, includes either anisocyanate group or an isocyanate-reactive group, such as a thiol groupand/or an aminic group. As used herein, “alkoxysilane” means a compoundcomprising a silicon atom, an alkoxy group and another organic group, inwhich the silicon atom is bonded with the organic group by a covalentbond.

For example, it is possible to make the silane-containingpolyester/polyurethane by reacting a polyol, such as the polymericpolyol (a) or an OH-functional prepolymer produced by reacting thepolymeric polyol (a) with a deficiency of isocyanate component (b), withan alkoxysilane comprising an isocyanate group. Examples of suchalkoxysilanes, which are suitable for use, include, for example,isocyanate-functional dialkoxysilanes and trialkoxysilanes, such as,isocyanatomethyltrimethoxysilane, isocyanatomethyltriethoxysilane,(isocyanatomethyl)methyldimethoxysilane,(isocyanatomethyl)methyldiethoxysilane,3-isocyanatopropyltrimethoxysilane,3-isocyanatopropylmethyldimethoxysilane,3-isocyanatopropyltriethoxysilane and3-isocyanatopropylmethyldiethoxysilane.

In this embodiment for producing the silane-containingpolyester/polyurethane, an OH-functional prepolymer can be produced byreaction of the polymeric polyol (a) with a deficiency of isocyanatecomponent (b), wherein an NCO:OH ratio of 1:1.3 to 1:10, such as 1:1.5to 1:3, is used.

Both the production of an OH-functional prepolymer and the reaction ofthe prepolymer with the alkoxysilane comprising an isocyanate group canbe accelerated by suitable catalysis. To accelerate the NCO—OH reaction,catalysts, such as organotin compounds or amine catalysts, are suitable.The catalyst, where incorporated, is often employed in quantities of0.001 to 5.0 wt. %, such as 0.001 to 0.1 wt. % and, in some cases, 0.005to 0.05 wt. %, based on the solids content of the process product.

The reaction is often carried out at temperatures of 20 to 200° C., suchas 40 to 120° C., or, in some cases, 60 to 100° C. The reaction may becontinued until complete conversion of the NCO groups of theisocyanate-containing compound is achieved. The progress of the reactioncan be monitored by means of suitable measuring instruments installed inthe reaction vessel and/or by means of analyses on samples taken.Appropriate methods include viscosity measurements, measurements of theNCO content, the refractive index and the OH content, gas chromatography(GC), nuclear magnetic resonance (NMR) spectroscopy, infrared (IR)spectroscopy and near-infrared (NIR) spectroscopy. The NCO content ofthe mixture is often determined by a titrimetric method.

The process may be carried out continuously, e.g. in a static mixer,extruder or kneader, or batchwise, e.g. in a stirred reactor.

Another process for the production of the crystalline or semicrystallinesilane-containing polyester/polyurethane is by reacting the isocyanatecomponent (b) or an NCO-functional prepolymer produced by reacting thepolymeric polyol (a) with an excess of isocyanate component (b) with analkoxysilane comprising an isocyanate-reactive group, such as an aminicgroups or a thiol group. In certain embodiments, the amounts of thecomponents used in the reaction to make such an NCO-functionalprepolymer are selected so as to provide an NCO:OH ratio of 1.3:1.0 to2:1, such as 1.5:1.0 to 2:1. As with the first process, thisurethanisation can also be accelerated by catalysis; the temperatureranges of the reaction are also analogous.

In this embodiment, the reaction is continued until complete conversionof the OH groups of the polyols is achieved. The progress of thereaction may be monitored by checking the NCO content and is completewhen the appropriate theoretical NCO content is reached. This can befollowed by suitable measuring instruments installed in the reactionvessel and/or by means of analyses on samples taken. Appropriate methodsviscosity measurements, measurements of the NCO content, the refractiveindex and the OH content, GC, NMR spectroscopy, IR spectroscopy and NIRspectroscopy. The NCO content of the mixture is often determined by atitrimetric method.

In these methods, an isocyanate component (b) and/or a NCO functionalprepolymer is reacted with an isocyanate-reactive alkoxysilane, such asan isocyanate-reactive dialkoxysilane and/or trialkoxysilane, including,for example, an aminic-functional alkoxysilane and/or thiol-functionalalkoxysilane, examples of which include, but are not limited to,mono-silanes and bis-silanes, specific examples of which include, butare not limited to, N(β-aminoethyl), γ-aminopropyltrimethoxysilane,bis(trimethoxysilylpropyl)amine, aminopropyltrimethoxysilane,mercaptopropyltrimethoxysilane, aminopropylmethyldimethoxysilane,mercaptopropylmethyldimethoxysilane, aminopropyltriethoxysilane,mercaptopropyltriethoxysilane, aminopropylmethyldiethoxysilane,mercaptopropylmethyldiethoxysilane, aminomethyltrimethoxysilane,aminomethyltriethoxysilane, (aminomethyl)methyldimethoxysilane,(aminomethyl)methyldiethoxysilane, N-butylaminopropyltrimethoxysilane,and/or N-phenylaminopropyltrimethoxysilane.

In certain embodiments, the component (c) is used in an amount of 0.1 to10 percent by weight, such as 0.2 to 2 percent by weight or, in somecases, 0.5 to 1.5 percent by weight, based on the total weight of thereactants used to make the polyester/polyurethane.

In certain embodiments, the crystalline or semicrystallinepolyester/polyurethane comprises a reaction product of reactants furthercomprising (d) a di- or poly-functional polyol with a molecular weightof from 62 to 399 g/mole. Examples of component (d) are polymers, suchas polyethers, polyesters, polycarbonates, polylactones and/orpolyamides. Also suitable for use as a component (d) are polyhydric,including dihydric, alcohols mentioned earlier with respect to thepreparation of the polyester polyols and include, for example, monomericpolyols such as ethanediol, diethylene glycol, 1,2-propanediol,dipropylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol,2,3-butanediol, 1,5-pentanediol and 1,6-hexanediol.

In certain embodiments, the component (d) is used in an amount of 0.1 to10 percent by weight, such as 0.1 to 2 percent by weight or, in somecases, 0.1 to 1 percent by weight, based on the total weight of thereactants used to make the polyester/polyurethane.

In certain embodiments, particularly those in which the crystalline orsemicrystalline polyester/polyurethane is sought to be present as astable dispersion in an aqueous composition, the crystalline orsemicrystalline polyester/polyurethane comprises a reaction product ofreactants further comprising (e) a dispersant compound that containsionic groups or potentially ionic groups, which may be either cationicor anionic in nature, and which has at least one isocyanate-reactivegroup, such as a hydroxyl, thiol, and/or aminic group. Suitable cationicand anionic groups include, for example, sulfonium groups, ammoniumgroups, phosphonium groups, carboxylate groups, sulfonate groups,phosphonate groups, or the corresponding non-ionic acid groups (i.e.,potentially ionic groups) that can be converted by deprotonation (i.e.,salt formation) into these groups.

Suitable ionic or potentially ionic compounds include, for example,mono- and di-hydroxycarboxylic acids; mono- and di-aminocarboxylicacids; mono- and di-hydroxysulfonic acids; mono- and di-aminosulfonicacids; mono- and di-hydroxyphosphonic acids; mono- anddi-aminophosphonic acids; and their salts, including combinationsthereof. Examples of suitable specific compounds include, withoutlimitation, dimethylolpropionic acid, dimethylolbutyric acid,hydroxypivalic acid; N-(2-aminoethyl)-p-alanine; 2-(2-aminoethylamino)ethanesulfonic acid; ethylenediame-propyl- or butyl-sulfonic acid; 1,2-or 1,3-propylenediamine-β-ethylsulfonic acid; citric acid; glycolicacid; lactic acid; glycine; alanine; taurine; lysine; 3,5-diaminobenzoicacid; an adduct of IPDI and acrylic acid and its alkali metal and/orammonium salts; an adduct of sodium bisulfite with but-2-ene-1,4-diol;polyethersulfonate; and the propoxylated adduct of 2-butenediol andNaHSC₃.

Suitable compounds for use in component (e) also include other2,2-bis(hydroxymethyl)alkane-carboxylic acids, such as dimethylolaceticacid and 2,2-dimethylolpentanoic acid, dihydroxysuccinic acid, Michaeladducts of acrylic acid with amines such as isophoronediamine orhexamethylenediamine, or mixtures of such acids and/ordimethylolpropionic acid and/or hydroxypivalic acid, sulfonic acid diolsoptionally comprising ether groups, for example, the compounds describedin U.S. Pat. No. 4,108,814 at col. 3, ln. 13 to col. 5, ln. 2, the citedportion of which being incorporated herein by reference.

Dispersant compounds reactive towards isocyanate groups may containhydrophilic ether groups that impart aqueous dispersability tomacromolecules covalently incorporating the dispersant compounds.Suitable compounds include, for example, polyether polyols and polyetherpolyamines. Exemplary compounds include, but are not limited to,alcohol-derived polyethylene glycols, polypropylene glycols, copolymersthereof, and monomethyl ethers thereof.

Suitable compounds for use in component (e) containing sulfonate orcarboxylate groups are, for example, diamino compounds or dihydroxycompounds which have sulfonate and/or carboxylate groups, such as, forexample, the sodium, lithium, potassium and tert-amine salts ofN-(2-aminoethyl)-2-aminoethanesulfonic acid, ofN-(3-aminopropyl)-2-aminoethanesulfonic acid, ofN-(3-aminopropyl)-3-aminopropanesulfonic acid, ofN-(2-aminoethyl)-3-aminopropanesulfonic acid, of the analogouscarboxylic acids, of dimethylolpropionic acid, of dimethylolbutyric acidor of the reaction products of a Michael addition of 1 mole of diamine,such as e.g. 1,2-ethanediamine or isophoronediamine, with 2 mole ofacrylic acid or maleic acid.

The acids are often employed directly in their salt form as sulfonate orcarboxylate. However, it is also possible for a proportion or the entireneutralizing agent needed for the salt formation to be first addedduring or after the preparation of the polyurethanes. Tert-amines whichare suitable for the salt formation are e.g. triethylamine,dimethylcyclohexylamine and/or ethyldiisopropylamine. Other amines canalso be employed for the salt formation, such as e.g. ammonia,diethanolamine, triethanolamine, dimethylethanolamine,methyldiethanolamine, aminomethylpropanol and also mixtures thereof.These amines are usually added only after the isocyanate groups havelargely reacted. It is also possible to employ other neutralizingagents, such as e.g. sodium, potassium, lithium or calcium hydroxide.

In certain embodiments, the component (e) is used in an amount of 0percent by weight to 20 percent by weight, such as 0.1 percent by weightto 20 percent by weight, 0.5 percent by weight to 20 percent by weightor, in some cases, 1 percent by weight to 15 percent by weight, based onthe total weight of the reactants used to make thepolyester/polyurethane.

In certain embodiments, the crystalline or semicrystallinepolyester/polyurethane comprises a reaction product of reactants furthercomprising a component (f) comprising an aminic chain extender, such asmonoamino and/or diamino compounds. Chain extenders in the context ofthe invention also include monoamines, which lead to chain termination,and mixtures thereof.

Examples of suitable monoamine chain extenders are aliphatic and/oralicyclic, primary and/or secondary monoamines such as ethylamine,diethylamine, the isomeric propyl- and butylamines, higherlinear-aliphatic monoamines and cycloaliphatic monoamines such ascyclohexylamine. Further examples are amino alcohols, i.e. compoundswhich contain amino and hydroxyl groups in one molecule, for exampleethanolamine, N-methylethanolamine, diethanolamine or 2-propanolamine.Further examples are monoamino compounds which additionally bearsulphonic acid and/or carboxy groups, for example taurine, glycine oralanine.

Examples of suitable diamino chain extenders are 1,2-ethanediamine,1,6-hexamethylenediamine,1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane (isophoronediamine),piperazine, 1,4-diaminocyclohexane or bis(4-aminocyclohexyl)methane. Inaddition, adipic dihydrazides, hydrazines or hydrazine hydrates areuseful. It is also possible to use polyamines such as diethylenetriaminein place of a diamino compound as a formation component.

In certain embodiments, component (f) is used in an amount of 0.1 to 10percent by weight, such as 0.1 to 2 percent by weight or, in some cases,0.1 to 1 percent by weight, based on the total weight of the reactantsused to make the polyester/polyurethane.

In certain embodiments, the crystalline or semicrystallinepolyester/polyurethane comprises a reaction product of reactants furthercomprising a component (g) comprising other isocyanate-reactivecompounds, such as aliphatic, cycloaliphatic or aromatic monoalcoholshaving 2 to 22 carbon atoms, such as ethanol, butanol, hexanol,cyclohexanol, isobutanol, benzyl alcohol, stearyl alcohol and2-ethylethanol; mono- or difunctional polyethers which are based onethylene oxide polymers or ethylene oxide/propylene oxide copolymersstarted on alcohols or amines and have a hydrophilizing action; blockingagents which are usual for isocyanate groups and can be split off againat elevated temperature, such as butanone oxime, dimethylpyrazole,caprolactam, malonates, triazole, dimethyltriazole,tert-butylbenzylamine and cyclopentanone carboxyethyl ester; andunsaturated compounds containing groups accessible for polymerizationreactions, such as hydroxyethyl acrylate, hydroxyethyl methacrylate,hydroxybutyl acrylate, hydroxybutyl methacrylate, hydroxypropylacrylate, hydroxypropyl methacrylate, pentaerythritol trisacrylate andhydroxy-functional reaction products of monoepoxides, bisepoxides and/orpolyepoxides with (meth)acrylic acid.

In some embodiments, the sum of the weight percentages of (a) through(g), or any subset thereof, such as the sum of (a) through (f), totals100%.

The crystalline or semicrystalline polyester/polyurethane can beprepared by any of a variety of processes, such asemulsifier/shear-force, acetone, prepolymer-mixing, melt-emulsification,ketimine, and spontaneous solids-dispersing processes, such as isdescribed in Methoden der Organischen Chemie, Houben-Weyl, 4th ed., Vol.E20/Part 2, p. 1682, Georg Thieme Verlag, Stuttgart, 1987.

In some embodiments, such as those in which the polyester/polyurethaneis provided as a stable dispersion in an aqueous composition, theacetone process is used to prepare the polyester/polyurethane. To thisend, prepolymers of components A and B, and if appropriate any of C, D,E, and/or G, are dissolved in acetone and chain-extended with componentF. After dispersion with water, the acetone is distilled off. Theacetone process is described in U.S. Pat. No. 3,479,310 and GB1,076,788. Other suitable processes for making aqueous polymericdispersions are described in DE-OS 2 725 589 and U.S. Pat. Nos.4,269,748, 4,192,937, 4,292,226, and 3,756,992.

Aqueous dispersions of crystalline or semicrystallinepolyester/polyurethanes that are suitable for use herein arecommercially available and include, for example, Dispercoll® U 53, U54,U 56 and U 8755, available from Covestro LLC, Pittsburgh, Pa.

As indicated, it was surprisingly discovered that the % UCS retention(measured as described in the Examples) of coated particle proppants ofthe present specification could be dramatically improved by inclusion ofjust a small amount (as described below) of such crystalline orsemicrystalline polyester/polyurethane in the coating. Thus, in certainembodiments, such crystalline or semicrystalline polyester/polyurethaneis present in an amount of just 0.01 to 1% by weight, such as 0.01 to0.5% by weight, 0.1 to 0.5% by weight, 0.1 to 0.4% by weight, or 0.2 to0.4% by weight, based on the total weight of the coated particles.

The coated particles of this specification may also include a solidparticle anti-clumping agent. Anti-clumping agents are materials that,when present in an effective amount, act to prevent the coated particlesof the present specification from clumping or aggregating, therebyenabling the production of free-flowing and pourable particles.

Suitable solid anti-clumping agents include, for example, silica, suchas fumed silica, organic bentonite, hydrogenated castor oil andpolyamides. In certain embodiments, the anti-clumping agents do notimpart any color to the coating when viewed by the naked eye and, assuch, do not act as a colorant.

In certain embodiments, the solid particle anti-clumping agent has anaverage particle size of at least 0.1 microns, such as at least 0.5microns and no more than 10 microns, such as no more than 5 microns.

In certain embodiments, the solid particle anti-clumping agent isemployed in an amount effective to produce free-flowing, pourableparticles. In certain embodiments, the solid particle anti-clumpingagent, such as fumed silica, is present in an amount of at least 0.1% byweight, such as 0.1 to 1% by weight or, in some cases, 0.1 to 0.4% byweight, based on the total weight of the coated particles.

Embodiments of the present specification are directed to methods ofmaking free-flowing particles. In some embodiments, the coated particlesdescribed herein are prepared by first drying the substrate particle,such as by, for example, heating the substrate particle to a temperatureof, for example, at least 50° C., such as at least 80° C. or at least90° C. If desired, an aminosilane, as described above, may be added tothe dried substrate particles, preferably while mixing. Theisocyanate-reactive composition is then added to the substrate particleswhile mixing, followed by addition of the isocyanate-functionalcomponent, and the condensation reaction is allowed to take place,followed by addition of an aqueous dispersion of a crystalline orsemicrystalline polyester/polyurethane, if used. Finally, the coatedparticles thereby produced are mixed with a solid particle anti-clumpingagent.

In certain embodiments, the reaction mixture is present in an amount ofat least 0.1% by weight, such as at least 1% by weight or at least 2% byweight and up to 10% by weight, up to 5% by weight, or, in some cases,up to 4% by weight, based on the total weight of substrate particles.The reaction mixture can be present in any amount between anycombination of these upper and lower values, inclusive, e.g., from 0.1to 10% by weight, 1% to 5% by weight, 2% to 5% by weight or 2% to 4% byweight, based on the total weight of substrate particles present.

It was also discovered, surprisingly, that a multi-step coating processcan dramatically improve the % UCS retention (measured as described inthe Examples) of coated particle proppants of the present specification.According to this process, the substrate particle is first dried, suchas by, for example, heating the substrate particle to a temperature of,for example, at least 50° C., such as at least 80° C. or at least 90° C.If desired, an aminosilane, as described above, may be added to thedried substrate particles, preferably while mixing. Then, a portion ofthe isocyanate-reactive composition, such as up to 50% by weight of thetotal amount to be used, is then added to the substrate particles whilemixing, followed by addition of a portion of the isocyanate-functionalcomponent, and the condensation reaction is allowed to take place.Thereafter, the remaining portion of the isocyanate-reactive compositionand the isocyanate-functional component are added, in one or moreadditional steps, followed by addition of an aqueous dispersion of acrystalline or semicrystalline polyester/polyurethane, if used. Finally,the coated particles thereby produced are mixed with a solid particleanti-clumping agent.

As will be appreciated, therefore, the present specification is alsodirected to methods for making coated particles that include (1) mixingsubstrate particles having a particle size of no more than 3 mesh (suchas any of those substrate particles described above) with a firstportion of an isocyanate-reactive composition (such as any of theisocyanate-reactive compositions described above) and a first portion ofa liquid isocyanate-functional component (such as any of the liquidisocyanate-functional components described above), (2) allowing acondensation reaction between the first portion of theisocyanate-reactive composition and the first portion of the liquidisocyanate-functional component to take place to form coated particles,and then (3) mixing the coated particles produced thereby with a second(and optionally a third) portion of the isocyanate-reactive compositionand a second (and optionally a third) portion of theisocyanate-functional component in one or more additional steps in whicha condensation reaction between each subsequent portion of theisocyanate-reactive composition added and each subsequent portion of theliquid isocyanate-functional component added is allowed to take placeprior to the addition of a further portion of the isocyanate-reactivecomposition and a further portion of the liquid isocyanate-functionalcomponent. Additional components, such as coupling agent, crystalline orsemicrystalline polyester/polyurethane and/or solid particleanti-clumping agent can be added as described above.

The coated particles described herein can be used in a variety ofapplications. In certain embodiments, however, the coated particles ofthe present specification are thought to be suitable for use inhydraulic fracturing a geologic formation. In these embodiments, thecoated particles may be combined with a carrier fluid, such as waterand/or a hydrocarbon, and the mixture injected at elevated pressure intoa well bore to an underground geologic formation. When the pressure inthe formation resulting from the injection exceeds the strength of theformation, a fracture is formed and the coated particles, i.e.,proppant, are placed in the formation in an effort to maintain thefracture in a propped position when the injection pressure is released.Upon ceasing the injection of fluid, it is desired that the proppantforms a pack that serves to hold open the fractures, thereby providing ahighly conductive channel through which a desired material, such aswater, oil, or gas (including natural gas) can flow to the well bore forretrieval.

In certain embodiments, therefore, the coated particles are used in amethod of forming a proppant composition that includes suspending thecoated particles described herein in a carrier fluid to form asuspension and injecting the suspension into an underground geologicformation.

The coated particles described herein can be injected as the soleproppant or as a partial replacement for an existing proppant. Forexample, if desired, the coated particles described herein may comprises1 to 99 percent by weight, such as 10 to 90 percent by weight, or, insome cases, 10 to 50 percent by weight, based on the total weight of theproppant present in the composition that is injected into the well bore.In some embodiments, an uncoated proppant is first placed in a well, andthereafter a proppant of the coated particles described herein is placedin the fracture nearest to the wellbore or fracture openings.

The coated particles of the present specification are presently thoughtto provide several advantages, particularly in the context of hydraulicfracturing. For example, the coated particles produced as describedherein are characterized by a very high UCS and good shelf stability,i.e., the ability to retain UCS over time as described in the Examples.

The non-limiting and non-exhaustive examples that follow are intended tofurther describe various non-limiting and non-exhaustive embodimentswithout restricting the scope of the embodiments described in thisspecification.

EXAMPLES Examples 1-8

All quantities given in “parts” and “percents” are understood to be byweight, unless otherwise indicated. The following materials were used inthe formulations of the examples:

Preparation of Coated Particles

Coated sand particles were produced using the ingredients and amounts(in parts) listed in Table 1.

TABLE 1 Component Example 1 Example 2 Example 3 Example 4 Example 5Example 6 Example 7 Example 8 SAND¹ 1362 1362 1362 1362 1362 1362 13621362 COUPLING 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 AGENT² POLYOL³ 26 26 26 2626 26 26 26 SURFACTANT⁴ 2.7 2.7 2.7 2.7 — — — — ISOCYANATE 1⁵ 16 16 1616 — — — — ISOCYANATE 2⁸ — — — — 16 16 — — ISOCYANATE 3⁹ — — — — — — 16— ISOCYANATE 4¹⁰ — — — — — — — 16 PUD⁶ 0 1 3 5 3 5 3 3 SILICA⁷ 2.7 2.72.7 2.7 2.7 2.7 2.7 2.7 ¹20/40 (20-40 mesh) sand²γ-aminopropyltriethoxysilane, commercially available from MomentivePerformance Materials ³a mixture of 70 parts by weight of Honey Bee ™Polyol HB-230 (a polyester polyol derived from soybean oil having ahydroxyl functionality of ~2 and hydroxyl number of 220-240 mg KOH/gmand having the structure described with reference to FIG. 4 of U.S. Pat.No. 8,828,269); 30 parts by weight of1-methyl-3,5-diethyl-2,4-diaminobenzene; 0.1 parts by weight of Dabco ®33-LV (an amine catalyst commercially available from Sigma-Aldrich); 0.1parts by weight of Dabco ® T-12 (dibutyltin dilaurate commerciallyavailable from Evonik); and 0.1 parts by weight of Reactint ® X17AB (apolymeric colorant commercially available from Milliken Chemical). ⁴Amixture of 73 parts by weight DAWN ® dish soap and 27 parts by weightwater. ⁵a urethane-modified diphenylmethane diisocyanate (PMDI)prepolymer having an NCO content of about 30.4, a functionality of about2.8, and a viscosity at 25° C. of 235-435 mPa · s that is prepared byreacting an excess of a polymethylene poly(phenyl isocyanate) with apolyester polyol having a number average molecular weight of about 450as described in U.S. Pat. No. 5,962,541. ⁶An aqueous dispersion of acrystalline anionic polyester/polyurethane, commercially available asDispercoll ® U 8755 from Covestro LLC. ⁷Untreated fumed silica,commercially available as CAB-O-SIL ® M5 available from Cabot. ⁸a mediumfunctionality p-MDI containing 65% by weight MDI and 29% by weight2,4-MDI, based on the total weight of MDI. ⁹a mixture of 2,2′-MDI,2,4′-MDI and 4,4-MDI that contains 55% by weight of 2,4′-MDI, based onthe total weight of MDI. ¹⁰a medium functionality p-MDI containing 49%by weight MDI and 28% by weight 2,4′-MDI, based on the total weight ofMDI.

To produce the coated sand particles, the SAND was pre-dried for aminimum of 2 hours in an oven heated to 93° C. The SAND was thentransferred to a suitable vessel, equipped with a mixer, and mixed at aslow speed. The COUPLING AGENT was then added to the SAND over a periodof about 15 seconds. Thereafter, the POLYOL was added over a period of30 seconds and the mixing speed was increased. Next, the SURFACTANT (ifused) was added over a period of 15 seconds, followed by addition ofISOCYANATE over a period of 30 seconds with increased mixing speed. ThePUD (if used) was then added over a period of 10 seconds and the coatedsand was allowed to mix at high speed for two minutes. The mixing wasthen stopped and the SILICA was added by dumping the SILICA into thecoated sand. Mixing was then resumed at high speed for two minutes andthen the mixing was stopped and the coated sand poured from the vessel.

Testing and Results.

The coated sands produced in examples 1-6 were tested to determine theirinitial UCS and their UCS after aging for 2 weeks at ambient conditions(about 20° C. (68° F.) and 1 atm absolute pressure (14.7 psia))(referred to below as “UCS Aged”) according to the following procedure.

80 grams of the coated sand (80 g) was mixed with 200 mL of a 2% KCl orlinear fluid and poured into 1⅛ inch long High Pressure High TemperatureSafe cell from Proptester, Inc. The liquid was drained and the cell waspressurized to 1000 psi using nitrogen and kept at that pressure for 24hours and 150° F. Afterwards, the cell was depressurized and the puckthus formed was carefully taken out and its strength tested by crushingthe consolidated proppant pack using an Instron® hydraulic press. Thepressure was applied slowly (100 psi/min) on the puck and the pressureat which the puck was catastrophically broken was recorded. The UCS loadin psi was recorded as the point where catastrophic failure of theconsolidated proppant pack occurred. Results are set forth in Table 2.

TABLE 2 % UCS Example No. UCS Initial UCS Aged Retention 1 200 psi (1379kPa) 60 psi (414 kPa) 30% 2 180 psi (1241 kPa) 75 psi (517 kPa) 42% 3180 psi (1241 kPa) 110 psi (758 kPa)  61% 4 180 psi (1241 kPa) 140 psi(965 kPa)  78% 5 200 psi (1379 kPa) 180 psi (1241 kPa) 90% 6 220 psi(1517 kPa) 209 psi (1441 kPa) 95% 7 195 psi (1344 kPa) 175 psi (1206kPa) 90% 8 150 psi (1034 kPa) 110 psi (7584 kPa) 73%

Examples 9-11

Preparation of Coated Particles

For Example 9, coated sand particles were produced using the ingredientsand amounts (in grams) listed in Table 3.

TABLE 3 Component Amount (in parts) SAND¹ 1362 COUPLING AGENT² 1.8POLYOL³ 8 SURLACTANT⁴ 3.6 ISOCYANATE 1⁵ 13 PUD⁶ — SILICA⁷ —

To produce the coated sand particles of Example 9, the SAND was firstcoated using the procedure described above for Examples 1-8, except thatthe PUD and SILICA additions were omitted.

To produce the coated sand of Example 10, 1391 grams of the coated sandproduced in Example 9, was mixed with 8 parts of POLYOL over 10 secondsand then 13 parts ISOCYANATE 1 was added over 10 seconds.

To produce the coated sand of Example 11, 1362 grams of the coated sandproduced in example 10, was mixed with 8 parts POLYOL over 10 secondsand then 13 parts ISOCYANATE 1 was added over 10 seconds. The mixing wasthen stopped and 2.7 parts of SILICA was added by dumping the SILICAinto the coated sand. Mixing was then resumed at high speed for twominutes and then the mixing was stopped and the coated sand poured fromthe vessel.

Testing and Results.

The coated sands produced in Examples 9-11 were tested to determinetheir initial UCS and their UCS Aged using the procedure described abovefor Examples 1-8. Results are in Table 4.

TABLE 4 % UCS Example No. UCS Initial UCS Aged Retention 1 200 psi (1379kPa) 60 psi (414 kPa)  30% 9 14 psi (97 kPa)  23 psi (159 kPa) 164% 10105 psi (724 kPa)  111 psi (765 kPa)  106% 11 250 psi (1724 kPa) 210 psi(1448 kPa)  84%

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

What is claimed is:
 1. A method of making coated particles comprising:(1) drying uncoated substrate particles having a particle size of nomore than 3 mesh by heating the uncoated substrate particles to atemperature of at least 50° C. to produce dried uncoated substrateparticles, (2) adding a coupling agent to the dried uncoated substrateparticles, (3) adding a first reaction mixture comprising anisocyanate-reactive composition and a liquid isocyanate-functionalcomponent to a mixture resulting from step (2), (4) allowing acondensation reaction between the isocyanate-reactive composition andthe liquid isocyanate-functional component to take place to form coatedparticles, (5) mixing the coated particles with a second reactionmixture comprising the isocyanate-reactive composition and theisocyanate-functional component, and (6) allowing a condensationreaction between the isocyanate-reactive composition and theisocyanate-functional component to take place to further coat the coatedparticles to form additionally coated particles, wherein theisocyanate-reactive composition comprises: (A) a plant oil polyesterpolyol; (B) an aromatic diamine; and (C) a catalyst for the reactionbetween hydroxyl groups and isocyanate groups, wherein the plant oilpolyester polyol is present in an amount of at least 60% by weight,based on the total weight of isocyanate-reactive components present inthe isocyanate-reactive composition and the aromatic diamine is presentin an amount of 10 to 40% by weight, based on the total weight of thetotal weight of isocyanate-reactive components present in theisocyanate-reactive composition.
 2. The method of claim 1, wherein thecoupling agent comprises an aminosilane.
 3. The method of claim 1,further comprising adding an aqueous dispersion of a crystalline orsemicrystalline polyester/polyurethane to the additionally coatedparticles.
 4. The method of claim 3, wherein the crystalline orsemicrystalline polyester/polyurethane has a decrystallizationtemperature of at least 35° C.
 5. The method of claim 3, furthercomprising mixing the additionally coated particles with a solidparticle anti-clumping agent.
 6. The method of claim 1, wherein up to50% by weight of the total isocyanate-reactive composition used in theprocess is mixed with the substrate particles in step (1).
 7. The methodof claim 1, wherein the liquid isocyanate-functional component comprisesa methylene diphenyl diisocyanate mixture comprising at least 10% byweight of 2,4′-methylene diphenyl diisocyanate and/or 2,2′-methylenediphenyl diisocyanate, based on the total weight of the mixture.
 8. Themethod of claim 1, wherein the substrate particles comprise sandparticles.
 9. The method of claim 1, wherein the first reaction mixtureand the second reaction mixture have an NCO Index of 180 to
 400. 10. Amethod of making coated particles comprising: (1) mixing substrateparticles having a particle size of no more than 3 mesh with a firstreaction mixture comprising an isocyanate-reactive composition and aliquid isocyanate-functional component, (2) allowing a condensationreaction between the isocyanate-reactive composition and the liquidisocyanate-functional component to take place to form coated particles,(3) mixing the coated particles with a second reaction mixturecomprising the isocyanate-reactive composition and theisocyanate-functional component; and (4) allowing a condensationreaction between the isocyanate-reactive composition and theisocyanate-functional component to take place to further coat the coatedparticles to form additionally coated particles, wherein theisocyanate-reactive composition comprises: (A) a plant oil polyesterpolyol; (B) an aromatic diamine; and (C) a catalyst for the reactionbetween hydroxyl groups and isocyanate groups, wherein the plant oilpolyester polyol is present in an amount of at least 60% by weight,based on the total weight of isocyanate-reactive components present inthe isocyanate-reactive composition and the aromatic diamine is presentin an amount of 10 to 40% by weight, based on the total weight of thetotal weight of isocyanate-reactive components present in theisocyanate-reactive composition, wherein the total reaction mixture usedis 0.1% to 10% by weight, based on the total weight of substrateparticles.
 11. The method of claim 10, wherein the total reactionmixture used is 1% to 5% by weight, based on the total weight ofsubstrate particles.
 12. The method of claim 11, wherein the totalreaction mixture used is 2% to 4% by weight, based on the total weightof substrate particles.
 13. A method of making coated particlescomprising: (1) mixing substrate particles having a particle size of nomore than 3 mesh with a first reaction mixture comprising anisocyanate-reactive composition and a liquid isocyanate-functionalcomponent, (2) allowing a condensation reaction between theisocyanate-reactive composition and the liquid isocyanate-functionalcomponent to take place to form coated particles, (3) mixing the coatedparticles with a second reaction mixture comprising theisocyanate-reactive composition and the isocyanate-functional component,(4) allowing a condensation reaction between the isocyanate-reactivecomposition and the isocyanate-functional component to take place tofurther coat the coated particles to form additionally coated particles,wherein the isocyanate-reactive composition comprises: (A) a plant oilpolyester polyol; (B) an aromatic diamine; and (C) a catalyst for thereaction between hydroxyl groups and isocyanate groups, wherein theplant oil polyester polyol is present in an amount of at least 60% byweight, based on the total weight of isocyanate-reactive componentspresent in the isocyanate-reactive composition and the aromatic diamineis present in an amount of 10 to 40% by weight, based on the totalweight of the total weight of isocyanate-reactive components present inthe isocyanate-reactive composition, and (5) adding an aqueousdispersion of a crystalline or semicrystalline polyester/polyurethane tothe additionally coated particles, wherein the aqueous dispersion of acrystalline or semicrystalline polyester/polyurethane is added in anamount such that the crystalline or semicrystallinepolyester/polyurethane is present in an amount of 0.01 to 1% by weight,based on the total weight of the additionally coated particles.
 14. Themethod of claim 13, wherein the aqueous dispersion of a crystalline orsemicrystalline polyester/polyurethane is added in an amount such thatthe crystalline or semicrystalline polyester/polyurethane is present inan amount of 0.1 to 0.4% by weight, based on the total weight of theadditionally coated particles.
 15. The method of claim 13, wherein thecrystalline or semicrystalline polyester/polyurethane has adecrystallization temperature of at least 35° C.
 16. The method of claim13, wherein the total reaction mixture used is 1% to 10% by weight,based on the total weight of substrate particles.
 17. The method ofclaim 13, further comprising, prior to step (1), drying substrateparticles by heating the substrate particles to a temperature of atleast 50° C.
 18. The method of claim 13, further comprising mixing theadditionally coated particles with a solid particle anti-clumping agent.